The present invention relates to a recording and reproducing apparatus for television signals.
A compressed band transmission system has been proposed in which a high-definition ("High Vision") video signal for producing a more definite image than the standard television system is transmitted by use of a channel of 27 MHz in band width of a broadcasting satellite.
Such a transmission system is reported in "A Single Channel Transmission System for HDTV Satellite Broadcasting (MUSE)", by Yuichi Ninomiya, et al., System Circuit Research Group for The Institute of Television Engineers of Japan, TEBS 95-2, March 22, 1984, The Report of the Institute, Vol. 7, No. 44.
In the transmission system discussed in the above-noted reference, a High Vision (high-definition TV) signal having an original band width more than 20 MHz is compressed to about 8 MHz by sub-Nyquist sampling for transmission. In the case of a still image, transmission of one image is completed with four fields, that is, two frames. As a result, the receiver contains a memory of two frames in terms of transmission signal rate, and an image is completed by inter-frame interpolation supplementation of a transmitted incoming television signal.
The above system, on the other hand, which compresses the television signal to the band width of about 8 MHz from more than 20 MHz, is useful for recording and reproduction as well as for the satellite broadcasting and therefore applications to VTR and video disk are considered. In the future, for the reproduction of these recorded signals, such a MUSE decoder of the receiver will be built in the body of VTR or video disk drive apparatus as the case may be, but for the time being it will continue to be used in combination with the receiver.
Conventionally, signal connection between a recording and reproducing system of a VTR, video disk or the like and the tuner or monitor is accomplished by a composite NTSC signal in analog form. Especially in the case of a High Vision signal, the image pick-up and recording are required in the base band of 20 MHz, and therefore the broad band signal processing including image contour compensation and time base collector requires digital signal processing. As a result, an analog-digital conversion or digital-analog conversion (hereinafter referred to as "A/D" or "D/A" respectively) is repeated each time as necessary, thus giving rise to the likelihood of a deteriorated image quality. Further, the MUSE decoder of the receiver processes signals digitally, and therefore if the interface with the receiver is taken with analog signals for recording in a VTR, an additional A/D or D/A process is required, thereby further deteriorating the image quality. Therefore, it is considered that the number of times of A/D and D/A operations may be reduced if the interface between the receiver and VTR is taken with digital signals. A block diagram for digital signal interface between units is shown in FIG. 2.
In FIG. 2, reference numeral 1 designates a BS tuner for receiving tuning and FM demodulating of the SHF wave for satellite broadcasting, numeral 2 an A/D converter for converting the demodulated signal to a digital signal, numeral 3 a digital preprocessing circuit for de-emphasis or the like, and numeral 4 an input signal change-over switch with a terminal connected to an output of the de-emphasis 3 and the other terminal for an external signal of VTR or the like. Numeral 5 designates a body of a MUSE decoder, numeral 6 a D/A converter, numeral 7 a monitor for displaying a high-definition signal, numeral 8 a signal processing section for expansion or the like processing along a time axis for VTR recording, numeral 9 a D/A converter, numeral 10 a recording and reproduction section for recording in or reproducing from tape or the like means by FM modulation and effecting FM demodulation, numeral 11 an A/D converter, and numeral 12 a signal processing section for time base compression for converting a time base expanded signal to the original MUSE signal in order for VTR recording or TBC for removing jitters of the reproduction signal. In FIG. 2, the parts designated by numerals 1 to 6 represent a receiver and those represented by numerals 8 to 12 a recording and reproduction system such as a VTR.
The advantage of taking digital instead of analog interface between the receiver and the recording and reproduction system is that the number of times of signal processing through the A/D and D/A converters is reduced by one respectively. In spite of this, the analog interface requires only one coaxial cable, whereas the digital version for 8-bit image data, for example, required ten signal cables including those for a clock signal and the earth (ground) line. Further, the lack of a reproduction FM signal called a "drop-out" which occurs in a VTR or the like is usually supplemented by the signal preceding by one horizontal scanning period (hereinafter called "1H") using a line memory within the VTR. In the case of MUSE signal, however, a signal preceding by two frames must be supplemented by use of a frame memory within the decoder, and for this purpose, an additional signal line is necessary for transmitting or informing a drop-out period from the VTR to the receiver. Most of the receivers and the recording and reproduction systems, by their nature, are consumer products, and therefore the number of their signal lines or the like should be decreased as much as possible. Also the recording and reproducing systems usually do not have or need not output a drop-out indicating pulse on the recording side, so it is desirable to use some other signal output connectors in common for such a pulse connector. In other words it is not desirable to add a signal line solely for transmission of drop out pulses.